The efficiency of a gas turbine engine may be improved by raising the turbine inlet gas temperature. At the present state of the art, such temperature is limited by the properties of known metals. Cooling air may be introduced to protect such metals when they are used to form parts of the turbine, but beyond a certain point, a trade-off of loss of air overrides the gain achieved by the use of the air.
Ceramic materials are currently under investigation for use in making turbine blades. There are major problems associated with the use of ceramic materials. Shapes and sizes are limited by manufacturing techniques and simplicity of shape is required to accommodate the low heat transfer characteristics of ceramic materials, to avoid stress rises due to the brittleness of the material, and to facilitate manufacturing of the blades themselves. Another major problem is to establish how to attach a ceramic blade to a rotor disk of metal. The common fir tree roots are not acceptable for use on ceramic turbine blades because of the low ductitility of ceramic materials which prevents substantially uniform distribution of loads to each land of such a root. Moreover, the metal rotor disk must be protected from exposure to the hot gases to which the blades are subjected.
Because of the problems mentioned above, a need has arisen for an improved means of mounting ceramic turbine blades on a metallic rotor disk of a turbine engine so that increased efficiency of the engine can be realized even though the turbine blades of the engine are formed from ceramic materials.